The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An aircraft is driven by several turbojet engines each housed in a nacelle accommodating an assembly of annex actuating devices related to its operation and providing various functions when the turbojet engine is in operation or at shutdown.
These annex actuating devices comprise in particular a thrust reversal mechanical system.
A turbojet engine nacelle generally has a substantially tubular structure comprising an air inlet upstream of the turbojet engine, a mid-section intended to surround a fan of said turbojet engine, a downstream section intended to surround the combustion chamber of the turbojet engine and optionally integrating thrust reversing means, and is generally terminated with an ejection nozzle the outlet of which is located downstream of the turbojet engine.
Modern nacelles are intended to accommodate a bypass turbojet engine capable of generating via the blades of the rotating fan a hot air flow (primary flow) and a cold air flow (secondary flow) which circulates outside the turbojet engine through an annular passage, also called flow path, formed between a fairing of the turbojet engine and an inner wall of the nacelle. The two air flows are ejected from the turbojet engine from the rear of the nacelle.
The role of a thrust reverser, during the landing of an aircraft, is to improve the braking ability thereof by redirecting forward at least a part of the air ejected from the turbojet engine. In this phase, the thrust reverser obstructs at least a part of the flow path of the cold flow and directs this flow to the front of the nacelle, therefore generating a counter-thrust which adds to the braking of the wheels and air brakes of the aircraft.
In general, the structure of a thrust reverser comprises a thrust reverser cowl displaceable between, on the one hand, a deployed position in which it opens a passage within the nacelle intended for the diverted air flow, and on the other hand, a retracted position in which it closes this passage.
In the case of a cascade-type thrust reverser, the reorientation of the air flow is performed by cascade vanes, associated with reversing flaps that block at least partially the air circulation flow path, the cowl having only a simple sliding function aiming to uncover or cover these cascade vanes.
The reversing flaps, also called blocking flaps, in turn, are activated and driven by slide of the movable cowl until obstructing at least partially the flow path downstream of the cascade vanes, so as to optimize reorientation of the cold air flow.
As is known, the cascade vanes are mounted on a front frame serving as a fixed portion of the thrust reversal device and fastened to a casing of the fan of the turbojet engine. This front frame also provides the support of actuating cylinders of the movable cowls.
Most often, the downstream section of the nacelle is made of two substantially semi-cylindrical semi-structures located, at the upper portion (called 12 hours), on both sides of an engine pylon of fastening of the turbojet engine to the aircraft and connected therebetween at the lower portion (called 6 hours).
The semi-structures are fastened to the engine pylon via an upper half-beam, and also comprise a lower half-beam. These lower and upper half-beams are equipped with slide rails for the thrust reversal movable cowl of the corresponding semi-structure.
For maintenance purposes, these semi-structures are pivotally mounted on the engine pylon about an axis substantially longitudinal of the nacelle via hinges. Latches at the lower portions provide the closing of the structure.
A nacelle having such a downstream structure having semi-cylindrical cowlings is commonly referred to as nacelle with a C or D duct (C-Duct or D-Duct).
Have also been developed nacelles called with an O structure (O-Duct) having a downstream structure that no longer exhibit two substantially semi-cylindrical semi-structures but one single substantially peripheral structure extending from one side of the engine pylon to the other side.
As a result, such a structure generally no longer exhibits two thrust reversal movable cowls but one single substantially peripheral cowl.
For maintenance purposes, such a downstream section no longer opens by the pivoting of the semi-structure about a substantially longitudinal axis of the nacelle but by downstream translation along this axis.
For a detailed description, one may refer to documents FR 2 911 372 and FR 2 952 681.
It will be noted in particular that for the purposes of the operations of maintenance and access to the combustion chamber of the turbojet engine, the front frame supporting the cascade vanes may in turn be disconnectable and moved backward with the outer cowling.
Furthermore, there are known called short O-Duct nacelle structures, in which the cascade vanes are also movably mounted in translation and able to be retracted at least partially along the thickness of the mid-section of the nacelle and thus overlap the fan casing when the thrust reverser is inactive, in the direct jet position. In the thrust reversal position, the cascade vanes are displaced with the movable cowl. The cascade vanes are hence no longer totally housed inside the movable cowl and thus occupy a less significant space which allows shortening it.
Besides a thrust reversal function, a reverser movable cowl belongs to the rear section and may exhibit a downstream portion forming an ejection nozzle.
The section of the ejection nozzle may be adapted depending on the different flight phases, namely, in particular, take-off, ascent, cruise, descent and landing in order to always preserve an optimal nozzle section depending on the turbojet engine speed. The nozzle will be then called variable nozzle.
Such a variable nozzle is associated with an actuating system allowing this section variation.
There are several solutions for realizing a variable nozzle.
A first solution is to provide pivoting terminal flaps mounted on the thrust reversal movable cowl and the pivoting of which is reflected in an increase or in a reduction of the outlet section. Such a system is described in particular in document FR 2 929 998.
There are also known panels movably mounted in translation inside the thrust reversal movable cowl, in a telescopic manner, the backward motion or the retraction of which similarly cause the increase or the reduction of the outlet section.
In such cases, the variable nozzle device has a dedicated actuating system, or a double-acting actuating system also associated with the reversal movable cowl.
Such solutions allow better accommodating the inner and outer aerodynamic lines of the nacelle and allow a better structural strength of the assembly.
In order to simplify the actuating systems and lighten the nacelle, another solution may also be envisaged thanks to the substantially conical shape of the back of the body of the nacelle: the thrust reversal movable cowl also provides by itself a variable nozzle function. The operation principle of such an arrangement is described in the document U.S. Pat. No. 5,655,360.
Although such an arrangement allows substantially lightening the rear section, its design involves some difficulties.
Indeed, during the displacement of the movable cowl in the nozzle mode, it should be provided that this displacement does not cause opening of the thrust reversing passage in the nacelle. Moreover, the movable cowl could be retracted in order to allow reducing the nozzle section relative to a nominal position.
This requires an overlay area at a rear end of the mid-section, an overlay area which generates an undesirable external aerodynamic accident.
Moreover, in the case of a thrust reversal system with retractable cascade vanes, a displacement of the movable cowl normally causes the concomitant displacement of the cascade vanes, or the displacement of said cascade vanes is useless during a displacement of the cowl in the nozzle mode.
Furthermore, the existing solutions may hardly be integrated with an O-Duct type nacelle with a peripheral thrust reverser cowl and this, either because of the installation of rails between the thrust reverser movable cowl and the outer structure which may be translated for maintenance purposes, or because of the complexity of the compatibility with the need to translate the assembly for accessing the engine compartment.